Aims and Objectives:
The choice of sampling methodology and number of sampling locations was based upon the priority given to meeting a number of potential objectives. These objectives can be divided into two categories - those that were concerned with the evaluation of the site for management purposes and those that sought to help with the interpretation of the ecology of Heron's Carr for education purposes.
Evaluation:
1. To evaluate the invertebrate interest of the site by comparison to similar
habitats both locally and nationally.
2. To discover if the proposed route of the boardwalk endangered
the survival of any particularly rare or threatened species.
3. To gather the necessary data to enable advice to be given on
how best to design the path of the boardwalk through the carr and
on the design of the boardwalk itself in order to maximise the invertebrate
interest of the site.
4. To make a quantitative comparison of the invertebrate fauna along the route of the
boardwalk before and after its construction.
5. From an evaluation of the impact of the boardwalk, to make recommendations for future management of the carr, paths and other linear features in order to maintain and if necessary enhance the invertebrate interest.
Interpretation:
1. To investigate the interaction between the structure of the vegetation and the different invertebrate communities that live in different habitats across the vegetational succession from open water through tussock sedge and carr to birch/ash woodland.
2. To show how particular groups, such as molluscs and beetles, can be used to indicate the relative importance of the site.
3. To show the temporal succession of different species and groups.
4. To make a detailed study of the invertebrates inhabiting particular features of the habitat, such as the 'pulk holes' and tussock structures.
Summary and Conclusions:
- Heron's Carr was found to be unexpectedly rich in invertebrate species. 242 species and 31 other taxa were recorded, but it was clear that the actual total might well have exceeded 1,500 species had all the habitats been sampled across the seasons and had all the groups been collected and identified.
- A surprising find was the unusually high number of fenland species living with the carr, including rarities such as Vertigo moulinsiana.
- The carr was sampled on two occasions, June and August, and there were considerable differences in both species-richness and abundance suggesting that many species were following patterns of occurrence linked to their particular life cycles.
- The sampling locations closest to the broad had the highest abundance of individuals in June as well as the highest number of species in August. This was probably linked to the distribution of tussock sedges which were found to harbour many invertebrate species. The sedgebeds in the central area of the carr were also comparatively species-rich.
- Aquatic macroinvertebrates along the littoral margin were far more numerous than in the littoral margin of the remainder of the broad and it was thought that this may have been on account of the very shallow water in Heron's Carr offering refuge from fish predation.
- A number of water beetles, a nymph of one Notable/Nb dragonfly, Sympetrum sanguineum, and three species of large-bodied cladocerans recorded from the lake littoral indicated that the water chemistry of Barton Broad was not overly enriched in the region of Heron's Carr.
- A number of unusual molluscs were recovered mainly from the central sedgebeds. These included Des Moulin's Whorl Snail, Vertigo moulinsiana, an RDB3 and BAP species and a number of other typically fenland species, such as Vertigo antivertigo and Zonitoides nitidus.
- Among the spiders were three Notable/Nb species - Philodromus albidus, Tetragnatha pinicola and Theridiosoma gemmosum. The presence of many long-jawed spiders, Tetragnatha sp., was again indicative of fenland conditions.
- One of the rarer woodlice, Ligidium hypnorum, was found frequently throughout the carr together with a number of other commoner species. A more thorough search of the tussocks in particular might have produced more species.
- The long-legged flies or Dolichipodidae, proved to be a very interesting group and produced the rarest species of the study, Dolichopus laticola, an RDB1 species. This species had only previously been recorded at Ormesby Broad and in the Bure Marshes.
- Difficulties with the use of the sweep net caused by the abundance of Succineid snails meant that craneflies and other delicate-winged insects could not be identified.
- 14 species of hoverfly were found that were mainly attracted to the yellow water traps. Six of these hoverfly species were described as Local. As was expected the hoverflies seemed to particularly favour the sunny glades within the carr where trees had toppled over leaving gaps in the canopy.
- Dragonflies and damselflies were neither caught nor observed in the study but they might have been flying high above the canopy or taking refuge higher up in the tree cover.
- Small battery-operated moth traps, known as Heath traps, were used on several occasions from June to September and one large trap was set at the nearby cottages. A total of 85 species were caught in the course of the study including one Notable/Nb species, the Cream-bordered Green Pea.
- The moth-trapping showed that the Heath traps were catching species mainly from the immediate locality and that most of the species were flying furthest away from the broad. The largest catch was collected on one of the stormiest nights of the year!
- Two Notable/Nb beetles were caught, a rove beetle, Oxytelus fulvipes and a ground beetle, Trechus rubens. A number of Local species were also collected including the Irish Flea Beetle, Aphthona nonstriata, the ground beetle Carabus granulatus, the marsh beetle Cyphon padi, the ant-like beetle Euconnus hirticollis and the two rove beetles Stenus bifovealatus and S. guttula..
- It was concluded that the effects of constructing a boardwalk through Heron's Carr would be unlikely to be detrimental to the invertebrate fauna provided that the work was carried out carefully and that sensitive areas were avoided.
- The most sensitive locations in our opinion were the tussock sedges close to the broad and the sedgebeds in the central area.
- Recommendations were made that in the course of construction and in its upkeep, the boardwalk should never threaten the structure and character of the carr, which should be left as intact as possible, and that certainly no heavy machinery should be used in the construction process
- As far as future management of Heron's Carr was concerned we would recommend a policy of non-intervention except perhaps the occasional clearance of some tree cover (should this not occur naturally) to encourage the growth of sedgebeds and tussocks.
- The results show that areas of open fen left to their own devices, and completely free from human intervention for a period of more than 50 years, need not suffer from depletion in invertebrate species-richness. In fact, the evidence from Heron's Carr suggested completely the opposite. These findings ought to have far-reaching implications with regards to future fen management strategies.
- Finally, in view of the not inconsiderable effort that went into this study, it is hoped that the information collected will be disseminated to as wide an audience as possible and perhaps incorporated into interpretative literature that could be provided to visitors using the boardwalk.
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